Method and system for color optimization in a display

ABSTRACT

Disclosed herein are iMoD displays optimized by utilizing different materials for one or more different color subpixels. Such optimized displays have improved color gamut over displays where all subpixels are constructed with the same material. Also disclosed are methods for manufacturing such displays and methods for optimizing iMoD displays.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application No.60/550,687, entitled “Method for Optimizing Color in IMOD Displays,”filed Mar. 6, 2004, which is incorporated herein by reference in itsentirety.

BACKGROUND

1. Field of the Invention

This invention relates to interferometric modulators (iMoDs). Moreparticularly embodiments of this invention relate to optimizing color iniMoD displays.

2. Description of the Related Art

To reach broad market acceptance, a display technology must be capableof providing the end-user with a satisfying visual experience. Themarket for high brightness, low power displays continues to expand withthe constant introduction of new portable electronic devices.Conventional wisdom suggests that reflective displays are unable toprovide the requisite image quality for broad market acceptance. Forexample, reflective liquid crystal displays (LCDs) suffer frominsufficient reflectance for office use without supplementalillumination and insufficient color gamut under conditions of brightsunlight. As a result, recent marketplace developments have shifted thedominant display for small mobile device applications from reflective totransflective LC displays. The increased brightness and color gamut oftransflective displays comes at the price of increased power consumptiondue to the near constant requirement for supplemental illumination,increased manufacturing complexity and increased costs.

SUMMARY

One aspect of the present invention is a display comprising a pluralityof pixels, where each pixel comprises a plurality of subpixels and eachsubpixel is selected from a plurality of subpixel types and where eachpixel comprises at least two subpixels that are of differing subpixeltype. Each subpixel type forms an interference modulator that is adaptedto reflect light of a different color than other subpixel types. Theinterference modulator of at least one subpixel type includes at leastone difference in its interference modulator components compared tointerference modulator components of at least one other subpixel type.

Another aspect of the present invention is a method of manufacturing adisplay comprising manufacturing an array of interference modulatorstructures on a substrate so as to generate at least two interferencemodulator structures having at least one difference in theirinterference modulator components. Each interference modulator structureis adapted to produce a respective color.

Still another aspect of the present invention is a method of optimizinga display where the color display comprises an array of interferencemodulator structures and each of the interference modulator structuresare capable of reflecting light of a particular color selected from agroup of colors. The optimization method comprises selecting materialsfor use in the interference modulator structures, selecting thethickness of the materials, and selecting the interference modulators'gap independently for each color in the group of colors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an iMoD structure.

FIG. 2 depicts an iMoD display consisting of pixels and subpixels.

FIGS. 3A and 3B depict two iMoD structures where the structure of FIG.3B contains an additional gold film.

FIG. 4 shows a CIE color space plot of the color space available for twoiMoD structures constructed with different materials.

FIG. 5 shows a CIE color space plot of the color parameters and colorgamut for three iMoD color displays having subpixels constructed withthe same material.

FIG. 6 shows the CIE color space of FIG. 4 with reflectance values as afunction of color for two iMoD structures constructed with differentmaterials.

FIG. 7 depicts a flowchart of a process for manufacturing an iMoDdisplay where at least one of the display's subpixels has a material notfound in the other subpixels.

FIG. 8 shows a CIE color space plot of the color parameters and colorgamut for two iMoD color displays having red subpixels constructed witha different material than the blue and green subpixels.

FIG. 9 depicts a flowchart of a process for separately optimizing eachcolor subpixel in an iMoD display.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

An alternative to reflective or transflective LCDs are displays based oniMoDs. In one embodiment, an iMoD reflective display is provided thatcomprises at least two different color subpixels. The color subpixelsare optimized so that the iMoD display produces a desired color gamut.Color optimization may be accomplished by choosing the materials ofcomponents, positioning of components, and thicknesses of componentsindependently for each subpixel. Independent color optimization ofsubpixels allows the manufacture of displays having a wider color gamutthan would be available if iMoDs having the same structure were used forall of the subpixels. Furthermore, color optimization provides iMoDdisplays having a wider color gamut than available in LCDs.

A basic iMoD structure is depicted, for example, in FIG. 1. A conductivepartially reflective mirror 502 is deposited unto transparent substrate500. Support structures 504 on substrate 500 support movable conductivemirror 506. Reflection from mirrors 502 and 506 can be observed fromview position 508. In an undriven state, a gap is formed between movablemirror 506 and partially reflective mirror 502. When a sufficientvoltage is applied across movable mirror 506 and partially reflectivemirror 502, movable mirror 506 collapses, closing the gap. Thus, forexample, FIG. 1 depicts movable mirror 506 in the collapsed state when avoltage of 7 volts is applied between the movable mirror 506 and thepartial reflector 502. Those of skill in the art will recognize thatvoltages other than 7 volts may be effective in collapsing movablemirror 506. In contrast, when 0 volts are applied, FIG. 1 illustratesthat there is a gap between movable mirror 506 and partial reflector502. The reflective spectral characteristics of the iMoD are dependentupon the optical path length between the movable mirror 506 and partialreflector 502, which depends on the size of the air gap and thethickness and index of refraction of any material disposed between themovable mirror 506 and partial reflector 502. In some embodiments, thepartially reflective mirror is coated with a dielectric layer such thatshorting of the movable mirror to the partially reflective mirror isprevented when the movable mirror collapses. The thickness of thedielectric can also determine the reflective spectral characteristics ofthe collapsed iMoD. Additional information on iMoD structures can befound in U.S. Pat. Nos. 5,835,255; 5,986,796; 6,040,937; 6,055,090;6,574,033; 6,589,625; 6,650,455; 6,674,562; 6,680,792; 6,710,908;6,741,377; and 6,794,119.

As will be apparent from the following description, the invention may beimplemented in any device that is configured to display an image,whether in motion (e.g., video) or stationary (e.g., still image), andwhether textual or pictorial. More particularly, it is contemplated thatthe invention may be implemented in or associated with a variety ofelectronic devices such as, but not limited to, mobile telephones,wireless devices, personal data assistants (PDAs), hand-held or portablecomputers, GPS receivers/navigators, cameras, MP3 players, camcorders,game consoles, wrist watches, clocks, calculators, television monitors,flat panel displays, computer monitors, auto displays (e.g., odometerdisplay, etc.), cockpit controls and/or displays, display of cameraviews (e.g., display of a rear view camera in a vehicle), electronicphotographs, electronic billboards or signs, projectors, architecturalstructures (e.g., tile layouts), packaging, and aesthetic structures(e.g., display of images on a piece of jewelry). More generally, theinvention may be implemented in electronic switching devices.

As described above, the gap between the partially reflective mirror 502and the movable mirror 506 determines the hue of light reflected from aniMoD by setting the difference in optical path length between lightreflected by the two mirrors. As used herein, “hue” refers to the colorperceived by a human observer of the reflected light. The resultingconstructive interference generates color from each iMoD. FIG. 2 depictsone embodiment of a color iMoD display 100. The iMoD display 100 may beconstructed by manufacturing an array of iMoD structures. The structuresmay be grouped into an array of pixels 102. Each pixel in the displaycomprises three iMoD structures, 104, 106, and 108, referred to as“subpixels.” The gap in each subpixel, 104, 106, or 108, is set so thatthe subpixel is capable of reflecting light in one of three primarycolors. Thus, each subpixel, 104, 106, or 108 may be of a different“subpixel type.” This gap is set during the manufacturing process bydepositing a sacrificial layer between the partial reflector 502 and themovable mirror 506 (see FIG. 1), which is ultimately removed during afinal ‘release’ etch process. Thus, the gap is designed into the display100 during fabrication by setting the parameters of the depositionprocess of the sacrificial material. In some embodiments, each iMoDelement 104, 106, or 108, operates as a binary device, switching betweena bright state and a dark state. The hue generated by a particular pixel102 will be determined by which subpixel(s) 104, 106, or 108, in thepixel 102 are in a bright state.

Alternatively, a monochrome iMoD display may be provided that includestwo or more subpixels types. For example, a cyan subpixel type and ayellow subpixel type may be provided to produce a white color by thecombination of the cyan and yellow colors. In one embodiment, amonochrome iMoD display is provided that comprises a single subpixeltype, such as a green subpixel type.

In some embodiments, each pixel 102 comprises more than three subpixels.In one embodiment, the additional subpixels may be adapted to generateadditional colors, thus providing additional subpixel types. In anotherembodiment, the additional subpixels may be adapted to generate the samethree primary colors. Thus, in this embodiment, the relative intensityof each primary color reflected by a pixel may be determined by how manysubpixels of that primary color are in a bright state.

Since the thickness of the sacrificial layer partially determines thecolor of iMoD elements, the possible set of generated colors is large.In addition, the particular set of colors available to be manufacturedinto an iMoD depends on the characteristics of the material used in theiMoD structure and the thickness of the materials used. For example, thematerial used for the movable mirror 506 may absorb certain wavelengthsof light, thus affecting the possible reflected colors. Similarly, thespectral absorption/reflection properties of the materials used for thepartial reflector 502, dielectric layers, and substrate 500 may affectthe set of colors available to be manufactured into an iMoD.

One example of iMoD structures consisting of different materials isdepicted in FIGS. 3A and 3B. FIG. 3A depicts an iMoD structure 170similar to that depicted in FIG. 1. A partial reflector 150 is depositedonto a substrate 152. Support structures 154 support a movable mirror156. In one embodiment, movable mirror 156 comprises aluminum, which isadvantageous due to its high reflectivity, low cost, and ease ofdeposition. The iMoD structure of FIG. 3A will be referred tohereinafter as “iMoD structure A.” FIG. 3B depicts an iMoD structure 180that has been modified by depositing an additional gold layer 160 on thealuminum movable mirror 156. The iMoD structure of FIG. 3B will bereferred to hereinafter as “iMoD structure B.” The gold layer 160 may bedeposited by metallic thin film layer deposition in an additionallithography step prior to deposition and patterning of the aluminumlayer 156. One of skill in the art will recognize that alternativematerials may be used to achieve the same result. For example, movablemirror 156 may be constructed of high reflectivity materials other thanaluminum. Furthermore, the iMoD structure B may be constructed by makingthe entire movable mirror 156 from gold rather than by adding theadditional gold layer 160 to aluminum.

As demonstrated below, the gold layer 160 improves the red subpixelsbecause it absorbs blue light. Alternative metals such as copper may beused to achieve a similar result. The absorption of blue light enablesthe use of more effective iMoD gap distances. Each iMoD gap distance iscapable of providing constructive interference for light reflected atwavelengths corresponding to integer multiples of twice the gapdistance. Thus, several wavelengths of light may be reflectedcorresponding to first order interference (wavelength=2× gap), secondorder interference (wavelength=gap), and so on. As discussed below, itis advantageous to use red subpixels with an iMoD gap distance tuned toreflect red light through second order interference. However, such gapdistances also reflect blue light through third order interference,inhibiting practical use of these red subpixel types when only analuminum movable mirror 156 is used. However, when the third order bluelight is absorbed by gold layer 160, the iMoD gap distances that producesecond order red light may be used.

Alternatively, absorption of blue light may be accomplished by includingcertain oxides that absorb blue light, such as HfO, in the iMoDstructure. For example, the oxides may be deposited onto the substrateas part of the iMoD structure of the red subpixels. The oxide layers areadvantageously transparent, thus acting as a filter for blue light whileletting light of other wavelengths proceed into the iMoD structure. Itwill be appreciated that reflectors and absorbers that absorb light atwavelengths other than blue may be similarly used to optimize subpixelsof colors other than red.

The color perceived from an iMoD subpixel (i.e., the hue) may expressedin terms of CIE tri-stimulus color parameters. CIE tri-stimulusparameters and methods for obtaining them are well known in the art. Invarious embodiments, these parameters may be expressed as X, Y, and Zvalues; x, y, and z values; Y, x, and y values; Y, u′, and v′ values; aswell as any other color parameters known in the art. In someembodiments, color parameter pairs such as (x,y) or (u′,v′) may be usedto graphically depict a given perceived color (i.e., hue) on atwo-dimensional CIE color space plot. FIG. 4 shows a (u′,v′) CIE colorspace plot with the possible set of colors that can be generated usingeither iMoD structure A 170 or iMoD structure B 180. The solid curve 200in FIG. 4 shows the possible set of colors that can be generated usingiMoD structure A 170. Each point on the curve 200 represents the colorgenerated by iMoD structure A 170 having a particular gap distancebetween the partial reflector 150 and the movable mirror 156. The gapdistance increases moving clockwise around the curve 200. In oneembodiment, each iMoD is capable of generating only one color, but thatcolor can come from any point along the curve shown in FIG. 4. In thisway, curve 200 represents the color design space from which the colorsof the red, green, and blue primary colors are chosen and thecorresponding gap distances of the subpixels 104 determined (see FIG.2). Curve 200 shows that changing the thickness of the gap over asufficient range can vary not only the hue but also the saturation(defined herein as the purity of the desired primary color hues) of theresulting colors. The more saturated colors are the result of secondorder constructive interference between the partial reflector and themovable mirror. FIG. 4 also indicates the color parameters for the limitof human perception as defined by the CIE 1976 color standard (longdashed line 202); red 204, blue 206, and green 208 EBU phosphor colorstandards (squares); a D65 white light source 210 (circle); and theprimary colors typically used for the subpixels of a reflective TFT LCDdisplay 212, 214, and 216 (diamonds).

To maximize the compatibility of iMoD fabrication with the existing LCDmanufacturing infrastructure, certain iMoD designs may utilize onlythose materials widely used by the LCD industry, such as aluminum forthe movable mirror 156. Furthermore, to reduce costs and employ thesimplest process, identical iMoD structures may be employed for allthree primary colors. In some embodiments of the present invention,alternative materials are used in constructing iMoD subpixels in orderto provide alternative color space options. A non-limiting example isthe utilization of gold layer 160 in iMoD structure B 180. In addition,in some embodiments, not all subpixels may be constructed of the samematerials, allowing greater flexibility in color optimization. Forexample, in one embodiment, red subpixels are manufactured according toiMoD structure B 180 while blue and green subpixels are manufacturesaccording to iMoD structure A 170.

Modifications to the thicknesses or materials comprising the componentsmaking up an iMoD can result in alternative color design spaces. Theshort-dashed curve 220 in FIG. 4 shows a set of design colors that canbe generated by iMoD structure B 180. As in curve 200 for iMoD structureA 170, each point on the curve 220 represents the color generated by aniMoD structure B iMoD 180 having a particular air gap. The air gapincreases moving clockwise around the curve 220. It can be seen that theaddition of gold layer 160 in iMoD structure B 180 results in theaccessibility of different (u′,v′) color parameters than are accessibleby iMoD structure A 170. In particular, iMoD structure B 180 can betuned to obtain color parameters near the EBU red phosphor 204 that areunavailable to iMoD structure A 170.

The design of an ideal display requires the balancing of image qualityparameters such as color gamut, brightness, and contrast. As usedherein, “color gamut” refers the range of perceived colors that can beproduced by a given display; “brightness” refers to the perceived amountof light reflected by a given display; and “contrast” refers to theperceived distinguishability between bright state reflectance and darkstate reflectance. In some cases, “color gamut” may be quantified by thearea of the triangle in a CIE color space plot whose vertices aredefined by the (u′,v′) color parameters for the red, blue, and greensubpixels, respectively. In some cases, “color gamut” may be compared tothe color gamut generated by the EBU red 204, blue 206, and green 208phosphors. This comparison may be quantified as a ratio of the area ofthe triangle in a CIE color space plot whose vertices are defined by the(u′,v′) color parameters for the red, blue, and green subpixels and thearea of the triangle in the CIE color space plot whose vertices aredefined by the EBU red 204, blue 206, and green 208 phosphors. In somecases, “contrast” may be quantified as the ratio of bright statereflectance to dark state reflectance, both measured under conditions ofdiffuse illumination.

The unique ability to adjust color in a continuous way affords iMoDdisplays wide latitude in performing optimization of color gamut,brightness, and contrast. For example, by choosing various combinationsof air gap sizes for iMoD subpixles, multiple color displays can beconstructed using the same iMoD structure design. FIG. 5 shows a CIE(u′,v′) color space plot of three iMoD displays constructed using iMoDstructure A 170. The three displays are illustrated by triangles in theCIE color space plot where the (u′,v′) color parameters of the primarycolor subpixles for each display define the vertices of the triangles.iMoD display 1 250 maximizes the reflectance of the display at the costof color gamut, iMoD display 3 252 maximizes the color gamut at the costof reflectance, while iMoD display 2 254 represents a compromise betweenthese competing parameters. The color gamut generated by EBU red 204,blue 206, and green 208 phosphors is also represented by triangle 256.

Table 1 lists various image quality parameters for iMoD display 1 250,iMoD display 2 254, and iMoD display 3 252. The reflectance ratio,defined as the percent of light reflected from the display, provides anindication of the relative brightness of the displays. The contrastratio indicates the contrast between bright and dark reflection. Thecolor gamut for the three displays is expressed as a percent of thecolor gamut generated when using EBU red 204, blue 206, and green 208phosphors (note the relative size of the triangles in the color spaceplot of FIG. 5 for iMoD display 1 250, iMoD display 2 254, and iMoDdisplay 3 252 as compared to color gamut 256 generated by the EBUphosphors). Table 1 also lists the (u′,v′) color parameters for the red,green, and blue subpixels chosen for iMoD display 1 250, iMoD display 2254, and iMoD display 3 252 as well as the respective projected whitecolor parameters. These results show the tradeoff between the colorgamut and the brightness and contrast of a reflective display with iMoDdisplay 1 250 having the highest reflectance and contrast ratio whileiMoD display 3 252 has the highest color gamut. TABLE 1 Image qualityparameters for iMoD displays 1-3, using iMoD structure A. Parameter iMoDdisplay 1 iMoD display 2 iMoD display 3 Reflectance ratio (%) 30 26 20Contrast ratio (x:1) 19 17 12 Color gamut 22 36 46 (% of EBU) Pixelpitch (mm) 0.231 0.231 0.231 Color White u′ 0.196 0.198 0.196 chroma- v′0.470 0.469 0.467 ticity Red u′ 0.346 0.347 0.349 v′ 0.528 0.528 0.528Green u′ 0.162 0.161 0.134 v′ 0.522 0.522 0.554 Blue u′ 0.178 0.1780.178 v′ 0.364 0.272 0.269

The color gamut results in Table 1 also show that iMoD displays arefully capable of generating a wide color gamut relative to typicalreflective LCDs. All of the parameters in Table 1 are determined forconditions of diffuse illumination, with reflectance measured 8 degreesfrom the normal to the display. This measurement technique isrecommended by the VESA measurement standards for reflective displays(see VESA, Flat Panel Display Measurements Standard, Version 2.0, 2001,Video Electronics Standards Association). Measuring display performanceunder diffuse illumination is representative of actual ambient viewingconditions.

Under conditions of diffuse illumination, iMoD displays can be twice asbright as typical reflective LCDs while providing a larger color gamut.Alternatively, iMoD displays can be designed to provide a color gamutcommensurate with that of transflective LCDs while in transmissive mode,all the while maintaining a reflectance greater than that of purelyreflective LCDs. These specifications exemplify the inherent flexibilityiMoD displays have in tailoring performance to each application. iMoDdisplays can address the need for low cost, single iMoD structure highreflectance displays (displays 1 250 and 2 254 of FIG. 5) as well as thebroader market for larger color gamut, high reflectance displays(display 3 252 of FIG. 5).

In one embodiment, the color in an iMoD display 100 consisting ofsubpixels 104, 106, and 108 constructed using identical iMoD structurematerials (i.e., the only difference between the subpixel types is thegap between the movable mirror 506 and the partial reflector 502) isoptimized to produce the desired characteristics (with references toFIGS. 1 and 2). For example, to provide a white point equivalent to astandard D65 white light source 210 (with reference to FIGS. 4 and 5), abalance exists between the selection of the green and red primarycolors. To maintain a green hue close to that of the EBU green phosphor208, the hue of the red primary may be shifted towards green.Alternatively, the red primary is set at a hue close to that of the redEBU phosphor 204, at the price of shifting the green primary towardsred. Once the primary colors are chosen, additional fine tuning of thewhite point and reflectance may be achieved by adjusting the area ratioof the three primary colors, for example by introducing multiplesubpixels of the same type (color). These choices of primary colors andarea ratios affect the overall brightness of the display 100. In oneembodiment, in order to maximize the brightness of the display 100, thegreen primary is set and the red primary is shifted towards green.

Increasing the Color Gamut by Combining Different iMoD Structures

The requirement of a balanced white point limits the choice of the redprimary color in the previous examples. While the iMoD is capable ofproducing red colors with a deeper, redder hue, these redder hues have alimited brightness. FIG. 6 shows a CIE color space plot of the possiblesets of color parameters that can be obtained from iMoDs constructedaccording to iMoD structure A 170 and iMoD structure B 180 (withreference to FIGS. 3A and 3B). FIG. 6 is the same plot as in FIG. 4except that reflectance values 300 for iMoDs having selected colorparameters in the red region are indicated on the curves for iMoDstructure A 200 and iMoD structure B 220. The reflectance for variousred subpixel choices using either iMoD structure A 170 or iMoD structureB 180 is indicated. When increasing the air gap in iMoD structure A 170(i.e., moving clockwise around curve 200), the reflectance fallssubstantially before the hue of the red EBU phosphor 240 is reached.However, increasing the air gap in iMoD structure B 180 (i.e., movingclockwise around curve 220) exhibits an alternative behavior, one inwhich the brightness of the red hue is maintained until the hue movesthrough the red shades and into the magenta and purple shades where theresponse of the eye is more limited.

While a single iMoD structure is capable of generating the high level ofperformance specified in Table 1, additional gains are possible. Bycombining primary colors from the color curve 200 (for iMoD structure A170) and the color curve 220 (for iMoD structure B 180) shown in FIGS. 4and 6 into one display, improvements in display image qualityperformance are possible. This results in improvements in the colorgamut, reflectance and contrast ratio, while maintaining full controlover the white point of the display.

Thus, in some embodiments, color displays (such as display 100 in FIG.2) are provided consisting of a plurality of iMoD structure subpixels(such as subpixels 104, 106, and 108 in FIG. 2) where at least one ofthe iMoD structure subpixels consists of an iMoD structure that isdifferent from the iMoD structures of the other subpixels. Non-limitingexamples of differences in the iMoD structures include a difference inmaterial chosen for one of the iMoD structure components, the additionor removal of a component, altering the thickness of a component in theiMoD structure, and/or a different order of components. Non-limitingexamples of components in the iMoD structure that can be altered includethe movable mirror 506, the partial reflector 502, dielectric layers,and the transparent substrate 500.

In some embodiments, a monochrome display whose bright state color isdetermined by the combination of two or more subpixels may be optimizedfor the monochrome color. For example, a monochrome white display maycomprise a cyan subpixel and a yellow subpixel whose combined colorsproduce white. The cyan and yellow subpixels may be independentlyoptimized as described herein in order to produce an optimized whitecolor.

In some embodiments, a monochrome display comprises a single colorsubpixel, however, that color subpixel is optimized as described hereinin order to produce a specific desired color. Similarly, in someembodiments, a single color subpixel or multiple color subpixels areoptimized in a color display so that the display is capable of producinga specific desired color with high quality. Thus, in some embodiments,color optimization is performed to achieve results other than just awide color gamut.

In cases where additional material is included in some iMoD structures,the additional material may comprise any material that has reflectionand/or absorption properties that enhance or suppress desiredwavelengths of light. The material may be metallic or non-metallic.

In some embodiments, differences in iMoD iMoD structures can be achievedby including additional deposition, patterning, and/or material removalsteps. For example, to include an additional film (such as film 160 inFIG. 3B) on the reflective side of the movable mirror 156, the film 160may be deposited prior to deposition of the movable mirror material 156.Lithographic patterning may then define which iMoD structures within thedisplay are to receive the additional film 160 (e.g., which of subpixels104, 106, and 108 in FIG. 2 are to receive the additional film). Themovable mirror material 156 may then be deposited followed by etching toremove the additional film 156 on selected iMoD structures. In someembodiments, the additional film 156 may be removed during the same“release” etch that removes the sacrificial layer.

FIG. 7 depicts a flowchart of one embodiment of a process formanufacturing iMoD structures. In this embodiment, an iMoD display 100such as in FIG. 2 is constructed where the pixels 102 have subpixels104, 106, and 108 and at least one of the subpixels 104, 106, and 108has a material not found in the other subpixels. In the first step 400,various initial material deposition, patterning, and/or removal stepsare optionally performed during which the same structures and materialsare created in all of the subpixels 104, 106, and 108. Next, at step402, the material that is to be selectively included in at least one ofthe subpixels is deposited. In step 404, this materials is patternedsuch as by using lithography so that it can be selectively removed oversome but not all of the subpixels. At step 406, other materialdeposition, patterning, and/or removal steps are optionally performed toall of the subpixels 104, 106, and 108. At step 408, a removal step isperformed to selectively remove the material deposited in step 402 inthe subpixels where the material is not to remain. In some embodiments,removal step 408 may also work to remove other material in some or allof the subpixels. Finally, in step 410, any additional materialdeposition, patterning, and/or removal steps are performed to all of thesubpixels 104, 106, and 108.

The increased flexibility provided by modifying iMoD structures inchoosing the primary colors for an iMoD display does not impact thedesign options available when choosing a brightness or color gamutlevel. FIG. 7 shows a CIE (u′,v′) color space plot depicting the colorgamut of two iMoD displays. The two displays (iMoD display 4 and iMoDdisplay 5) are illustrated by triangles in the CIE color space plotwhere the (u′,v′) color parameters of the primary color subpixles foreach display define the vertices of the triangles. Triangle 350corresponds to iMoD display 4 and triangle 352 corresponds to iMoDdisplay 5. The blue and green subpixels of the two displays wereconstructed using iMoD structures 170 while the red subpixles wereconstructed using iMoD structures 180. The color gamut generated by EBUred 204, blue 206, and green 208 phosphors is also represented bytriangle 256.

Table 2 lists various image quality parameters for iMoD display 4 350and iMoD display 5 352. As in Table 1, the reflectance ratio, defined asthe percent of light reflected from the display, provides an indicationof the relative brightness of the displays. The contrast ratio indicatesthe contrast between bright and dark reflection. The color gamut for thethree displays is expressed as a percent of the color gamut generatedwhen using EBU red 204, blue 206, and green 208. Table 2 also lists the(u′,v′) color parameters for the red, green, and blue subpixels chosenfor iMoD display 4 350 and iMoD display 5 352 as well as the respectiveprojected white color parameters. Table 2 demonstrates that iMoD display4 350 has a reflectance ratio and contrast ratio comparable to iMoDdisplay 1 250 in Table 1 while exhibiting a much higher color gamut.Similarly, iMoD display 5 352 exhibits a high color gamut with onlymodest decrease in reflectance ratio and contrast ratio. By replacingthe red subpixel in iMoD displays 1, 2 and 3 with a subpixel constructedwith an iMoD structure 180, the chromaticity of the red primary hasdramatically shifted towards and beyond the hue of the red EBU phosphorin displays 4 350 and 5 352. This result provides an improved usefulcolor gamut as the range of bright, accessible red hues is increased.TABLE 2 Image quality parameters of iMoD displays 4 and 5, using iMoDstructures A and B. Parameter iMoD display 4 iMoD display 5 Reflectanceratio (%) 30 24 Contrast ratio (x:1) 18 15 Color gamut (% of EBU) 39 50Pixel pitch (mm) 0.231 0.231 Color chromaticity White u′ 0.200 0.198 v′0.469 0.469 Red u′ 0.370 0.372 v′ 0.469 0.496 Green u′ 0.161 0.133 v′0.522 0.555 Blue u′ 0.179 0.178 v′ 0.274 0.271

Table 3 details the image quality parameters for iMoD display 4 350 andiMoD display 5 352 in comparison with typical reflective andtransflective TFT LCDs measured under conditions of diffuseillumination. Comparison of the image quality performance of iMoDdisplays 4 350 and 5 with typical conventional reflective ortransflective LCDs shows dramatic differences. iMoD displays are capableof providing reflectance levels more than twice that of reflective TFTLCDs while simultaneously providing a larger color gamut. The more thandoubling of the brightness of the display has a dramatic effect upon theusage model of reflective displays. iMoD reflective displays with theirlow power benefits can be easily read in poorly lit office space withoutthe need for supplemental illumination. Furthermore, the increasedefficiency of the iMoD display lowers the requisite luminance requiredof the supplemental illumination system for dark ambient reading. Poweris saved both by the bi-stable nature of the iMoD display and by theminimal dependence upon supplemental illumination. TABLE 3 Typical imagequality parameters for reflective and transflective LC displays.Transflective Transflective TFT LCD in TFT LCD in iMoD iMoD Reflectivereflective emissive display display Parameter TFT LCD mode mode 4 5Reflectance 15 <10 NA 30 24 ratio (%) Contrast 15 10 NA 18 14 ratio(x:1) Color gamut 18 6 46 39 50 (% of EBU) Pixel pitch 0.242 0.224 0.2240.231 0.231 (mm)

The iMoD displays also look favorable when compared with transflectiveLCDs. The nature of the transflective compromise necessitates the use ofthe backlight under all conditions except bright outdoor sunlight. Whilein this transmissive mode, the display is capable of providing a brightimage with a large color gamut (˜46% of the EBU color gamut). However,while in a purely reflective mode, the reflectance falls to 10% or less,while the color gamut falls to 6% of the EBU color gamut. Alternatively,iMoD display 5 352 is capable of providing a reflectance level greaterthan 20% and a color gamut of 50% of the EBU color gamut all the whilein a purely reflective mode. Supplemental illumination in the case ofthe iMoD display can increase the color gamut of the display in asimilar manner as for the transflective display.

Methods of Optimizing Displays

In some embodiments, methods are provided for optimizing color iMoDdisplays (such as display 100 in FIG. 2). As described in more detailabove, the color reflected from a particular iMoD structure can be tunedby varying the materials making up the iMoD structure as well asselecting the interference gap in the iMoD structure. Thus, methods areprovided that include individually selecting materials and gaps for eachcolor subpixel (such as subpixels 104, 106, and 108 in FIG. 2) in aniMoD display. Such selections can be made based on modeling ofinterference properties and material spectral properties. In addition oralternatively, before complete iMoD displays are fabricated, initialimage quality performance studies can be performed upon iMoD teststructures. These structures can then provide the opportunity tooptimize the iMoD structure and quantify the color performance ofdifferent iMoD designs.

One embodiment of individually optimizing each color subpixel in an iMoDdisplay is depicted in the flowchart of FIG. 9. At step 450, one of thedesired subpixel colors is selected (e.g., red, green, or blue). At step452, the materials to be used to construct the various elements in theiMoD for that subpixel are selected. These materials may be selected soas to optimize are particular characteristic of the color reflected fromthat subpixel (e.g., selecting gold for use in the movable mirror iniMoD structure B 180 in FIG. 3B). In step 454, the thickness of eachmaterial is chosen, keeping in mind the desired reflectance, contrast,and color characteristics for that color subpixel. In step 456, the airgap for the selected subpixel is determined based on the desired colorcharacteristics for that subpixel. In decision step 458, it isdetermined if there are any other color subpixels that are to beincluded in the display and that have not yet been optimized. If so, theprocess returns to block 450 for optimization of that subpixel. If not,the process proceeds to block 460 for termination of the optimization.

1. A display, comprising: a plurality of pixels, each pixel comprising aplurality of subpixels, wherein each subpixel is selected from aplurality of subpixel types and each pixel includes at least twosubpixels that are of differing subpixel type; wherein each subpixeltype forms an interference modulator that is adapted to reflect light ofa different color than other subpixel types; and wherein theinterference modulator of at least one subpixel type includes at leastone difference in its interference modulator components compared tointerference modulator components of at least one other subpixel type.2. The display of claim 1, wherein said at least one difference is adifference in an optical component.
 3. The display of claim 2, whereinsaid optical component includes an optical film.
 4. The display of claim3, wherein said optical film is metallic.
 5. The display of claim 3,wherein said optical film is non-metallic.
 6. The display of claim 1,wherein the group of subpixel types includes subpixels that reflectsubstantially cyan light and subpixels that reflect substantially yellowlight.
 7. The display of claim 1, wherein the group of subpixel typesincludes subpixels that reflect substantially red light, subpixels thatreflect substantially green light, and subpixels that reflectsubstantially blue light.
 8. The display of claim 7, wherein the redsubpixel type includes at least one difference in its interferencemodulator components compared to the interference modulator componentsof the green and blue subpixel types.
 9. The display of claim 8, whereinthe difference in the red subpixel type's interference modulatorincludes a metallic layer that is not present in the interferencemodulators of the green and blue subpixel types.
 10. The display ofclaim 9, wherein the metallic layer is positioned on a movable mirror inthe red subpixel type's interference modulator.
 11. The display of claim9, wherein the metallic layer is selected from the group consisting ofgold and copper.
 12. The display of claim 1, wherein said at least onedifference includes an additional component not found in theinterference modulator components of the at least one other subpixeltype.
 13. The display of claim 12, wherein the additional component ispositioned adjacent to a movable mirror.
 14. The display of claim 12,wherein the additional component is positioned adjacent to a partialreflector.
 15. The display of claim 12, wherein the additional componentis positioned adjacent to a dielectric layer.
 16. The display of claim12, wherein the additional component is positioned adjacent to asubstantially transparent substrate.
 17. The display of claim 12,wherein the additional component is a metallic layer.
 18. The display ofclaim 17, wherein the additional component is selected from the groupconsisting of gold and copper.
 19. The display of claim 1, wherein saidat least one difference includes an interference modulator componentconstructed of a different material than a corresponding component foundin the interference modulator of the at least one other subpixel type.20. The display of claim 19, wherein the interference modulatorcomponent constructed of a different material is a movable mirror. 21.The display of claim 20, wherein said different material includes ametal selected from the group consisting of gold and copper.
 22. Thedisplay of claim 19, wherein the interference modulator componentconstructed of a different material is a partial reflector.
 23. Thedisplay of claim 19, wherein the interference modulator componentconstructed of a different material is a dielectric layer.
 24. Thedisplay of claim 19, wherein the interference modulator componentconstructed of a different material is a substantially transparentsubstrate.
 25. The display of claim 1, wherein said at least onedifference comprises an interference modulator component of a differentthickness than a corresponding component found in the interferencemodulator of the at least one other subpixel type.
 26. The display ofclaim 25, wherein the interference modulator component of a differentthickness is a movable mirror.
 27. The display of claim 25, wherein theinterference modulator component of a different thickness is a partialreflector.
 28. The display of claim 25, wherein the interferencemodulator component of a different thickness is a dielectric layer. 29.The display of claim 25, wherein the interference modulator component ofa different thickness is a substantially transparent substrate.
 30. Thedisplay of claim 1, wherein said at least one difference comprisesinterference modulator components arranged in a different order thancorresponding components found in the interference modulator of the atleast one other subpixel type.
 31. A method of manufacturing a display,comprising manufacturing an array of interference modulator structureson a substrate so as to generate at least two interference modulatorstructures having at least one difference in their interferencemodulator components, wherein each interference modulator structure isadapted to produce a respective color.
 32. The method of claim 31,wherein said at least one difference is generated by deposition andpatterning of a material.
 33. The method of claim 31, wherein said atleast one difference is a difference in an optical component.
 34. Themethod of claim 33, wherein said optical component includes an opticalfilm.
 35. The method of claim 34, wherein said optical film is metallic.36. The method of claim 34, wherein said optical film is non-metallic.37. The method of claim 31, wherein said at least one differenceincludes an additional component in one of the two interferencemodulator structures that is not found in the interference modulatorcomponents of the other of the two interference modulator structures.38. The method of claim 37, wherein the additional component ispositioned adjacent to a movable mirror.
 39. The method of claim 37,wherein the additional component is positioned adjacent to a partialreflector.
 40. The method of claim 37, wherein the additional componentis positioned adjacent to a dielectric layer.
 41. The method of claim37, wherein the additional component is positioned adjacent to asubstantially transparent substrate.
 42. The method of claim 37, whereinthe additional component is a metallic layer.
 43. The method of claim42, wherein the metallic layer is selected from the group consisting ofgold and copper.
 44. The method of claim 31, wherein said at least onedifference includes an interference modulator component in one of thetwo interference modulator structures constructed of a differentmaterial than a corresponding component found in the other of the twointerference modulator structures.
 45. The method of claim 44, whereinthe interference modulator component constructed of a different materialis a movable mirror.
 46. The method of claim 45, wherein said differentmaterial includes a metal selected from the group consisting of gold andcopper.
 47. The method of claim 44, wherein the interference modulatorcomponent constructed of a different material is a partial reflector.48. The method of claim 44, wherein the interference modulator componentconstructed of a different material is a dielectric layer.
 49. Themethod of claim 44, wherein the interference modulator componentconstructed of a different material is a substantially transparentsubstrate.
 50. The method of claim 31, wherein said at least onedifference includes an interference modulator component in one of thetwo interference modulator structures having a different thickness thana corresponding component found in the other of the two interferencemodulator structures.
 51. The method of claim 50, wherein theinterference modulator component of a different thickness is a movablemirror.
 52. The method of claim 50, wherein the interference modulatorcomponent of a different thickness is a partial reflector.
 53. Themethod of claim 50, wherein the interference modulator component of adifferent thickness is a dielectric layer.
 54. The method of claim 50,wherein the interference modulator component of a different thickness isa substantially transparent substrate.
 55. The method of claim 31,wherein said at least one difference includes interference modulatorcomponents in one of the two interference modulator structures arrangedin a different order than corresponding components found in the other ofthe two interference modulator structures.
 56. The method of claim 31,wherein said manufacturing includes a plurality of material depositionsteps, a plurality of patterning steps, and at least one materialremoval step and wherein at least one of said patterning steps and atleast one of said material removal steps are used to generate said atleast one difference.
 57. A display manufactured according to the methodof claim
 31. 58. A method of manufacturing a display, said displaycomprising an array of interference modulator structures, each of saidinterference modulator structures capable of reflecting light of aparticular color selected from a group of colors, said methodcomprising: selecting materials for use in the interference modulatorstructures, selecting thickness of said materials, and selecting theinterference modulators' gap independently for each color in said groupof colors.
 59. The method of claim 58, wherein said group of colorsincludes a substantially red color, a substantially green color, and asubstantially blue color.
 60. The method of claim 58, wherein said groupof colors includes a substantially cyan color and a substantially yellowcolor, and wherein said selecting steps are performed so that thecombination of said cyan color and said yellow color produce a desiredwhite color.
 61. The method of claim 58, wherein at least one materialselected for at least one color in said group of colors differs frommaterials selected for at least one other color in said group of colors.62. The method of claim 61, wherein said at least one material isselected from the group consisting of gold and copper.
 63. The method ofclaim 58, wherein at least one material selected for at least one colorin said group of colors differs in thickness from a correspondingmaterial selected for at least one other color in said group of colors.64. A display manufactured according to the method of claim
 58. 65. Adisplay manufactured by a process comprising, manufacturing at least twointerference modulator structures on a substrate so as to generate atleast two interference modulator structures having at least onedifference in their interference modulator components, wherein eachinterference modulator structure is adapted to produce a respectivecolor.
 66. The display of claim 65, wherein said at least one differenceis generated by deposition and patterning of a material.
 67. The displayof claim 65, wherein said at least one difference is a difference in anoptical component.
 68. The display of claim 67, wherein said opticalcomponent includes an optical film.
 69. The display of claim 68, whereinsaid optical film is metallic.
 70. The display of claim 68, wherein saidoptical film is non-metallic.
 71. The display of claim 65, wherein saidat least one difference includes an additional component in one of thetwo interference modulator structures that is not found in theinterference modulator components of the other of the two interferencemodulator structures.
 72. The display of claim 71, wherein theadditional component is positioned adjacent to a movable mirror.
 73. Thedisplay of claim 71, wherein the additional component is positionedadjacent to a partial reflector.
 74. The display of claim 71, whereinthe additional component is positioned adjacent to a dielectric layer.75. The display of claim 71, wherein the additional component ispositioned adjacent to a substantially transparent substrate.
 76. Thedisplay of claim 71, wherein the additional component is a metalliclayer.
 77. The display of claim 76, wherein the metallic layer isselected from the group consisting of gold and copper.
 78. The displayof claim 65, wherein said at least one difference includes aninterference modulator component in one of the two interferencemodulator structures constructed of a different material than acorresponding component found in the other of the two interferencemodulator structures.
 79. The display of claim 78, wherein theinterference modulator component constructed of a different material isa movable mirror.
 80. The display of claim 79, wherein said differentmaterial includes a metal selected from the group consisting of gold andcopper.
 81. The display of claim 78, wherein the interference modulatorcomponent constructed of a different material is a partial reflector.82. The display of claim 78, wherein the interference modulatorcomponent constructed of a different material is a dielectric layer. 83.The display of claim 78, wherein the interference modulator componentconstructed of a different material is a substantially transparentsubstrate.
 84. The display of claim 65, wherein said at least onedifference includes an interference modulator component in one of thetwo interference modulator structures having a different thickness thana corresponding component found in the other of the two interferencemodulator structures.
 85. The display of claim 84, wherein theinterference modulator component of a different thickness is a movablemirror.
 86. The display of claim 84, wherein the interference modulatorcomponent of a different thickness is a partial reflector.
 87. Thedisplay of claim 84, wherein the interference modulator component of adifferent thickness is a dielectric layer.
 88. The display of claim 84,wherein the interference modulator component of a different thickness isa substantially transparent substrate.
 89. The display of claim 65,wherein said at least one difference includes interference modulatorcomponents in one of the two interference modulator structures arrangedin a different order than corresponding components found in the other ofthe two interference modulator structures.
 90. The display of claim 65,wherein said manufacturing includes a plurality of material depositionsteps, a plurality of patterning steps, and at least one materialremoval step and wherein at least one of said patterning steps and atleast one of said material removal steps are used to generate said atleast one difference.
 91. A display comprising an array of interferencemodulator structures, each of said interference modulator structurescapable of reflecting light of a particular color selected from a groupof colors, said display manufactured by a method comprising: selectingmaterials for use in the interference modulator structures, selectingthickness of said materials, selecting the interference modulators' gapindependently for each color in said group of colors, and constructingsaid interference modulator structures based on said selectings.
 92. Thedisplay of claim 91, wherein said group of colors includes asubstantially red color, a substantially green color, and asubstantially blue color.
 93. The display of claim 91, wherein saidgroup of colors includes a substantially cyan color and a substantiallyyellow color, and wherein said selecting steps are performed so that thecombination of said cyan color and said yellow color produce a desiredwhite color.
 94. The display of claim 91, wherein at least one materialselected for at least one color in said group of colors differs frommaterials selected for at least one other color in said group of colors.95. The display of claim 94, wherein said at least one material isselected from the group consisting of gold and copper.
 96. The displayof claim 91, wherein at least one material selected for at least onecolor in said group of colors differs in thickness from a correspondingmaterial selected for at least one other color in said group of colors.